Download ACC/AHA 2007 Guidelines on Perioperative Cardiovascular

ACCF/AHA 2009 Perioperative Focused
Update & Guideline
Based on the 2009 ACCF/AHA Focused Update on
Perioperative Beta Blockade Incorporated Into the ACC/AHA
2007 Guidelines on Perioperative Cardiovascular Evaluation
and Care for Noncardiac Surgery:
A Report of the ACC/AHA Task Force on Practice Guidelines developed
in collaboration with the Amer. Society of Echocardiography, Amer.
Society of Nuclear Cardiology, Heart Rhythm Society, Society of
Cardiovascular Anesthesiologists, Society for Cardiovascular
Angiography and Interventions, Society for Vascular Medicine, and
Society for Vascular Surgery
ACCF/AHA 2009 Guidelines on Perioperative
Cardiovascular
Evaluation and Care for Noncardiac Surgery
This slide set was adapted from the 2009 ACCF/AHA
Focused Update on Perioperative Beta Blockade
Incorporated Into the ACC/AHA 2007 Guidelines on
Perioperative Cardiovascular Evaluation and Care for
Noncardiac Surgery (Journal of the American College of
Cardiology published ahead of print on November 2, 2009,
available at
http://content.onlinejacc.org/cgi/content/full/j.jacc.2009.07.010)
The full-text guidelines are also available on the Web sites:
ACC (www.acc.org) and,
AHA (www.americanheart.org)
Special Thanks to
The 2007 Periop Guidelines Writing Committee Members
Lee A. Fleisher, MD, FACC, FAHA, Chair
Joshua A. Beckman, MD, FACC
William K. Freeman, MD, FACC
Kenneth A. Brown, MD, FACC, FAHA
James B. Froehlich, MD, MPH, FACC
Hugh Calkins, MD, FACC, FAHA
Edward K. Kasper, MD, FACC
Elliott Chaikof, MD
Judy R. Kersten, MD, FACC
Kirsten E. Fleischmann, MD, MPH, FACC
Barbara Riegel, DNSc, RN, FAHA
John F. Robb, MD, FACC
The 2009 Periop Focused Update Writing Committee Members
Kirsten E. Fleischmann, MD, MPH, FACC, chair
Joshua A. Beckman, MD, FACC
James B. Froehlich, MD, MPH, FACC
Christopher E. Buller, MD, FACC
Edward K. Kasper, MD, FACC, FAHA
Hugh Calkins, MD, FACC, FAHA
Judy R. Kersten, MD, FACC
Lee A. Fleisher, MD, FACC, FAHA
John F. Robb, MD, FACC, FAHA
William K. Freeman, MD, FACC
R. James Valentine, MD
Applying Classification of Recommendations
and Level of Evidence
Class I
Class IIa
Class IIb
Class III
Benefit >>> Risk
Benefit >> Risk
Additional studies with
focused objectives
needed
Benefit ≥ Risk
Additional studies with
broad objectives needed;
Additional registry data
would be helpful
Risk ≥ Benefit
No additional studies
needed
Procedure/ Treatment
SHOULD be
performed/
administered
IT IS REASONABLE to
perform
procedure/administer
treatment
Procedure/Treatment
MAY BE CONSIDERED
Procedure/Treatment
should NOT be
performed/administered
SINCE IT IS NOT HELPFUL
AND MAY BE HARMFUL
Alternative Phrasing:
should
is recommended
is indicated
is useful/effective/
beneficial
is reasonable
can be useful/effective/
beneficial
is probably recommended or
indicated
may/might be considered
may/might be reasonable
usefulness/effectiveness is
unknown /unclear/uncertain
or not well established
is not recommended
is not indicated
should not
is not
useful/effective/beneficial
may be harmful
Applying Classification of Recommendations
and Level of Evidence
Class I
Class IIa
Class IIb
Class III
Benefit >>> Risk
Benefit >> Risk
Additional studies with
focused objectives
needed
Benefit ≥ Risk
Additional studies with
broad objectives needed;
Additional registry data
would be helpful
Risk ≥ Benefit
No additional studies
needed
Procedure/ Treatment
SHOULD be
performed/
administered
IT IS REASONABLE to
perform
procedure/administer
treatment
Procedure/Treatment
MAY BE CONSIDERED
Level of Evidence:
Level A:
Data derived from multiple randomized clinical trials or meta-analyses
Multiple populations evaluated
Level B:
Data derived from a single randomized trial or nonrandomized studies
Limited populations evaluated
Level C:
Only consensus of experts opinion, case studies, or standard of care
Very limited populations evaluated
Procedure/Treatment
should NOT be
performed/administered
SINCE IT IS NOT HELPFUL
AND MAY BE HARMFUL
Active Cardiac Conditions for Which the Patient Should
Undergo Evaluation and Treatment Before Noncardiac
Surgery (Class 1, LOE: B)
Condition
Examples
Unstable coronary
syndromes
 Unstable or severe angina* (CCS class III or IV)†
 Recent MI‡
Decompensated HF (NYHA
functional class IV;
worsening or new-onset HF)
Significant arrhythmias
Severe valvular disease
 High-grade atrioventricular block
 Mobitz II atrioventricular block
 Third-degree atrioventricular heart block
 Symptomatic ventricular arrhythmias
 Supraventricular arrhythmias (including atrial fibrillation) with
uncontrolled ventricular rate (HR > 100 bpm at rest)
 Symptomatic bradycardia
 Newly recognized ventricular tachycardia
 Severe aortic stenosis (mean pressure gradient > 40 mm Hg,
aortic valve area < 1.0 cm2, or symptomatic)
 Symptomatic mitral stenosis (progressive dyspnea on exertion,
exertional presyncope, or HF) or MVA<1.5 cm2
CCS indicates Canadian Cardiovascular Society; HF, heart failure; HR, heart rate; MI, myocardial infarction; NYHA, New York Heart
Association. *According to Campeau.10 †May include stable angina in patients who are unusually sedentary. ‡The ACC National
Database Library defines recent MI as more than 7 days but within 30 days)
Estimated Energy Requirements for
Various Activities
Can You…
1 Met
Take care of yourself?
Eat, dress, or use the toilet?
Walk indoors around the
house?
Can You…
4 Mets Climb a flight of stairs or walk up
a hill?
Walk on level ground at 4 mph
(6.4 kph)?
Do heavy work around the house
like scrubbing floors or lifting or
moving heavy furniture?
Walk a block or 2 on level
ground at 2 to 3 mph (3.2 to
4.8 kph)?
4 Mets
Do light work around the house
like dusting or washing dishes?
> 10
Mets
Participate in moderate
recreational activities like golf,
bowling, dancing, doubles tennis,
or throwing a baseball or
football?
Participate in strenuous sports
like swimming, singles tennis,
football, basketball, or skiing?
MET indicates metabolic equivalent; mph, miles per hour; kph, kilometers per hour. *Modified from Hlatky et al, copyright 1989, with
permission from Elsevier, and adapted from Fletcher et al.
Cardiac Evaluation and Care Algorithm for
Noncardiac Surgery (1)
Step 1
Need for emergency
noncardiac surgery?
Yes
(Class I, LOE C)
Operating room
Perioperative surveillance
and postoperative risk
stratification and risk factor
management
No
Step 2
Active cardiac
conditions*
Yes
(Class I, LOE B)
Evaluate and treat per
ACC/AHA guidelines
Consider
operating room
No
Step 3
Low risk surgery
Yes
(Class I, LOE B)
Proceed with
planned surgery
No
Step 4
Functional capacity greater than or
equal to 4 METs without symptoms.‡
Yes
(Class IIa, LOE B)
Proceed with
planned surgery
Cardiac Evaluation and Care Algorithm for
Noncardiac Surgery (2)
Step 5 No or unknown
3 or more clinical
risk factors?
Vascular Surgery
1-2 clinical
risk factors?
Intermediate
risk surgery
Vascular Surgery
Intermediate risk
surgery
Class IIa,
LOE B
Consider testing if it will
change management ¶
No clinical
?
risk factors
Class I
LOE B
Proceed with
Proceed with planned surgery with HR control ¶ (Class IIa, LOE B)
or consider noninvasive testing (Class IIb LOE B) if it will change with
management
planned surgery
Cardiac Risk Stratification for Noncardiac
Surgical Procedures
Risk Stratification
Procedure Examples
Vascular (reported cardiac
Aortic and other major vascular surgery
risk often > 5%)
Peripheral vascular surgery
Intermediate (reported
Intraperitoneal and intrathoracic surgery
cardiac risk generally 1%-5%)
Carotid endarterectomy
Head and neck surgery Orthopedic surgery
Prostate surgery
Low† (reported cardiac
Endoscopic procedures
risk generally <1%
Superficial procedure /Breast surgery
Cataract surgery
Ambulatory surgery
Prognostic Gradient of Ischemic Responses During
an ECG-Monitored Exercise Test in Patients With
Suspected or Proven CAD
High Risk Ischemic Response
Ischemia induced by low-level exercise* (less than 4 METs or
heart rate < 100 bpm or < 70% of age-predicted heart rate)
manifested by 1 or more of the following:
•
•
•
•
•
•
Horizontal or downsloping ST depression > 0.1 mV
ST-segment elevation > 0.1 mV in noninfarct lead
Five or more abnormal leads
Persistent ischemic response >3 minutes after exertion
Typical angina
Exercise-induced decrease in systolic BP by 10 mm Hg
Prognostic Gradient of Ischemic Responses During
an ECG-Monitored Exercise Test in Patients With
Suspected or Proven CAD
Intermediate:
Ischemia induced by moderate-level exercise (4 to 6 METs or HR 100 to 130
bpm (70% to 85% of age-predicted heart rate)) manifested by > 1 of the
following:
•
•
•
Horizontal or downsloping ST depression > 0.1 mV
Persistent ischemic response greater than 1 to 3 minutes after exertion
3- 4 abnormal leads
Low
No ischemia or ischemia induced at high-level exercise (> 7 METs or HR >130
bpm (> 85% of age-predicted heart rate)) manifested by:
•
•
Horizontal or downsloping ST depression > 0.1 mV
1- 2 abnormal leads
Inadequate test
Inability to reach adequate target workload or heart rate response for age
without an ischemic response. For patients undergoing noncardiac surgery, the
inability to exercise to at least the intermediate-risk level without ischemia
should be considered an inadequate test.
Recommendations for Preoperative
Noninvasive Evaluation of LV Function
I IIa IIb III
I IIa IIb III
It is reasonable for patients with dyspnea
of unknown origin to undergo
preoperative evaluation of LV function.
It is reasonable for patients with current
or prior HF with worsening dyspnea or
other change in clinical status to
undergo preoperative evaluation of LV
function if not performed within 12
months.
Recommendations for Preoperative
Noninvasive Evaluation of LV Function
I IIa IIb III
I IIa IIb III
Reassessment of LV function in clinically
stable patients with previously
documented cardiomyopathy is not well
established.
Routine perioperative evaluation of LV
function in patients is not
recommended.
Recommendations for Preoperative
Resting 12-Lead ECG
Preoperative resting 12-lead ECG is recommended
for patients with:
I IIa IIb III
• At least 1 clinical risk factor* who are
undergoing vascular surgical procedures.
I IIa IIb III
• Known CHD, peripheral arterial disease, or
cerebrovascular disease who are undergoing
intermediate-risk surgical procedures.
* Clinical risk factors include history of ischemic heart disease, history of compensated or prior HF, history of cerebrovascular disease, diabetes
mellitus, and renal insufficiency.
Recommendations for Preoperative
Resting 12-Lead ECG
I IIa IIb III
Preoperative resting 12-lead ECG is reasonable in
persons with no clinical risk factors who are
undergoing vascular surgical procedures.
I IIa IIb III
Preoperative resting 12-lead ECG may be reasonable
in patients with at least 1 clinical risk factor who are
undergoing intermediate-risk operative procedures.
I IIa IIb III
Preoperative and postoperative resting 12-lead ECGs
are not indicated in asymptomatic persons undergoing
low-risk surgical procedures.
Recommendations for Noninvasive Stress
Testing Before Noncardiac Surgery
I IIa IIb III
Patients with active cardiac conditions in whom
noncardiac surgery is planned should be evaluated
and treated per ACC/AHA guidelines before
noncardiac surgery.
I IIa IIb III
Noninvasive stress testing of patients with 3 or more
clinical risk factors and poor functional capacity (< 4
METs) who require vascular surgery is reasonable if
it will change management.
Recommendations for Noninvasive Stress
Testing Before Noncardiac Surgery
I IIa IIb III
Noninvasive stress testing may be considered for patients:
• With at least 1 to 2 clinical risk factors and poor
functional capacity (less than 4 METs) who require
intermediate-risk or vascular surgery if it will change
management.
I IIa IIb III
Noninvasive testing is not useful for patients:
• With no clinical risk factors undergoing intermediaterisk noncardiac surgery.
• Undergoing low-risk noncardiac surgery.
Preoperative Coronary Revascularization With
CABG or Percutaneous Coronary Intervention
Coronary revascularization before noncardiac
surgery is useful in patients with stable angina
who have:
I IIa IIb III
● significant left main coronary artery stenosis
● 3-vessel disease (survival benefit is greater when
LVEF <0.50)
● 2-vessel disease with significant proximal
LAD stenosis & either EF<0.50 or demonstrable
ischemia on noninvasive testing.
Coronary revascularization before noncardiac surgery
is recommended for patients with:
● high-risk UA/NSTEMI
● acute STEMI
Preoperative Coronary Revascularization With
CABG or Percutaneous Coronary Intervention
I IIa IIb III
I IIa IIb III
In patients in whom coronary revascularization with PCI
is appropriate for mitigation of cardiac symptoms & who
need elective noncardiac surgery in the subsequent 12
months, a strategy of balloon angioplasty or bare-metal
stent placement followed by 4-6 weeks of dual-antiplatelet
therapy is probably indicated.
In patients who have received DES & who must undergo
urgent surgical procedures that mandate the discontinuation
of thienopyridine therapy, it is reasonable to continue ASA if
at all possible & restart the thienopyridine as soon as
possible.
Preoperative Coronary Revascularization With
CABG or Percutaneous Coronary Intervention
The usefulness of preoperative coronary
revascularization is not well established in:
I IIa IIb III
High risk ischemic patients (e.g. abnormal
dobutamine stress echo with at least
5 segments of wall-motion abnormalities)
I IIa IIb III
Low risk ischemic patients with an
abnormal dobutamine stress echo
(segments 1-4)
Preoperative Coronary Revascularization With
CABG or Percutaneous Coronary Intervention
It is not recommended that routine prophylactic coronary
revascularization be performed in patients with stable CAD
before noncardiac surgery
I IIa IIb III
Elective noncardiac surgery is not recommended within:
● 4-6 weeks of bare metal coronary stent
implantation or within 12 months of drug-eluding
coronary stent implantation in patients in whom
thienopyridine therapy, or ASA & thienopyridine
therapy, will need to be discontinued
perioperatively.
● 4 weeks of coronary revascularization with
balloon angioplasty
Drug Eluting Stents (DES) and Stent
Thrombosis
A 2007 AHA/ACC/SCAI/ACS/ADA science advisory report concludes that
premature discontinuation of dual antiplatelet therapy markedly increases the
risk of catastrophic stent thrombosis and death or MI.
To eliminate the premature discontinuation of thienopyridine therapy, the
advisory group recommends the following:
•
Before implantation of a stent, the physician should discuss the need for
dual-antiplatelet therapy. In patients not expected to comply with 12
months of thienopyridine therapy, whether for economic or other reasons,
strong consideration should be given to avoiding a DES.
•
In patients who are undergoing preparation for PCI and who are likely to
require invasive or surgical procedures within the next 12 months,
consideration should be given to implantation of a bare metal stent or
performance of balloon angioplasty with provisional stent implantation
instead of the routine use of a DES.
Drug Eluting Stents (DES) and Stent
Thrombosis
•
A greater effort by healthcare professionals must be made before patient
discharge to ensure that patients are properly and thoroughly educated about
the reasons they are prescribed thienopyridines and the significant risks
associated with prematurely discontinuing such therapy.
•
Patients should be specifically instructed before hospital discharge to contact
their treating cardiologist before stopping any antiplatelet therapy, even if
instructed to stop such therapy by another healthcare provider.
•
Healthcare providers who perform invasive or surgical procedures and who are
concerned about periprocedural and postprocedural bleeding must be made
aware of the potentially catastrophic risks of premature discontinuation of
thienopyridine therapy. Such professionals who perform these procedures
should contact the patient’s cardiologist if issues regarding the patient’s
antiplatelet therapy are unclear, to discuss optimal patient management
strategy.
Drug Eluting Stents (DES) and Stent
Thrombosis
•
Elective procedures for which there is significant risk of perioperative
or postoperative bleeding should be deferred until patients have
completed an appropriate course of thienopyridine therapy (12
months after DES implantation if they are not at high risk of bleeding
and a minimum of 1 month for bare-metal stent implantation).
•
For patients treated with DES who are to undergo subsequent
procedures that mandate discontinuation of thienopyridine therapy,
aspirin should be continued if at all possible and the thienopyridine
restarted as soon as possible after the procedure because of concerns
about late stent thrombosis.
Proposed Approach to the Management of Patients
with Previous PCI Who Require Noncardiac Surgery
Previous PCI
Balloon
angioplasty
Drug-eluting
stent
Bare-metal
stent
<365 days
Time since PCI
<14 days
Delay for elective or
nonurgent surgery
PCI, percutaneous coronary intervention
>14 days
>30- 45 days
Proceed to the
operation room
with aspirin
<30- 45 days
Delay for elective or
nonurgent surgery
>365 days
Proceed to the
operating room
with aspirin
Proposed Treatment for Patients Requiring PCI
Who Need Subsequent Surgery
Acute MI, H risk ACS, or
H risk cardiac anatomy
Bleeding risk of surgery
low
Stent & continue dual
antiplatelet therapy
Not low
Timing of surgery
14-29 days
Balloon
angioplasty
30-365 days
Bare-metal
stent
>365 days
Drug-eluting
stent
Recommendations for Beta-Blocker
Medical Therapy
I IIa IIb III
Beta blockers should be
continued in patients
undergoing surgery who are
receiving beta blockers for
treatment of conditions with
ACCF/AHA Class I guideline
indications for the drugs
Recommendations for Beta-Blocker
Medical Therapy
I IIa IIb III
I IIa IIb III
Beta blockers titrated to heart rate and blood
pressure are probably recommended for patients
undergoing vascular surgery who are at high
cardiac risk owing to coronary artery disease or
the finding of cardiac ischemia on preoperative
testing (4, 5).
Modified
Beta blockers titrated to heart rate and blood
pressure are reasonable for patients in whom
preoperative assessment for vascular surgery
identifies high cardiac risk, as defined by the
presence of > 1 clinical risk factor.*
Modified
Recommendations for Beta-Blocker
Medical Therapy
I IIa IIb III
Beta blockers titrated to heart rate and blood
pressure are reasonable for patients in whom
preoperative assessment identifies coronary
artery disease or high cardiac risk, as defined
by the presence of > 1 clinical risk factor,*
who are undergoing intermediate-risk surgery.
NO CHANGE
Recommendations for Beta-Blocker
Medical Therapy
I IIa IIb III
The usefulness of beta blockers is uncertain
for patients who are undergoing either
intermediate-risk procedures or vascular
surgery in whom preoperative assessment
identifies a single clinical risk factor in the
absence of coronary artery disease.*
NO CHANGE
I IIa IIb III
The usefulness of beta blockers is uncertain
in patients undergoing vascular surgery with
no clinical risk factors who are not currently
taking beta blockers.
NO CHANGE
Recommendations for Beta-Blocker
Medical Therapy
I IIa IIb III
Beta blockers should not be given to patients
undergoing surgery who have absolute
contraindications to beta blockade.
NO CHANGE
I IIa IIb III
Routine administration of high-dose beta
blockers in the absence of dose titration is
not useful and may be harmful to patients
not currently taking beta blockers who are
undergoing noncardiac surgery.
New
Clinical Risk Factors for Perioperative
Cardiovascular Complications
Those used in our 2009 recommendations, are unchanged from the
2007 document and include the following:
• history of ischemic heart disease
• history of compensated or prior heart failure;
• history of cerebrovascular disease;
• diabetes mellitus; and
• renal insufficiency (defined in the Revised Cardiac Risk Index as a
preoperative serum creatinine of >2 mg/dL)
Recommendations for Perioperative BetaBlocker Therapy
Surgery
No Clinical Risk
Factors
CAD or High Risk
(1 or more
clinical risk
factors)
Patients
Currently Taking
Beta Blockers
Class llb, Level of
Evidence: B
Class lla, Level of
Evidence: B
Class 1, Level of
Evidence: C
Intermediate risk
…
Class lla, Level of
Evidence: B
Class 1, Level of
Evidence: C
Low risk
…
…
Class 1, Level of
Evidence: C
Vascular
Recommendations for Statin Therapy
I IIa IIb III
I IIa IIb III
I IIa IIb III
For patients currently taking statins and scheduled for
noncardiac surgery, statins should be continued.
For patients undergoing vascular surgery with or
without clinical risk factors, statin use is reasonable.
For patients with at least 1 clinical risk factor who are
undergoing intermediate-risk procedures,
statins may be considered.
Recommendations for Alpha-2 Agonists
I IIa IIb III
I IIa IIb III
Alpha-2 agonists for perioperative control of
hypertension may be considered for patients
with known CAD or at least 1 clinical risk factor
who are undergoing surgery.
Alpha-2 agonists should not be given to patients
undergoing surgery who have contraindications
to this medication.
Recommendations for PA Catheters &
Anesthetic agents
Preoperative intensive care monitoring with a pulmonary
I IIa IIb III artery catheter for optimization of hemodynamic status
might be considered; however, it is rarely required and
should be restricted to a very small number of highly
selected patients whose presentation is unstable and
complex and who have multiple comorbid
conditions.
It can be beneficial to use volatile anesthetic agents during
noncardiac surgery for the maintenance of general
anesthesia in hemodynamically stable patients at risk for
myocardial Ischemia (Class IIa, level B).
Recommendations for IV Nitro
I IIa IIb III
The usefulness of intraoperative nitroglycerin as a
prophylactic agent to prevent myocardial ischemia and
cardiac morbidity is unclear for high-risk patients
undergoing noncardiac surgery, particularly those who
have required nitrate therapy to control angina. The
recommendation for prophylactic use of nitroglycerin
must take into account the anesthetic plan and patient
hemodynamics and must recognize that vasodilation and
hypovolemia can readily occur during anesthesia and
surgery.
Use of TEE and Maintenance of Body
Temperature
I IIa IIb III
The emergency use of intraoperative or perioperative TEE
is reasonable to determine the cause of an acute,
persistent, and life-threatening hemodynamic
abnormality.
I IIa IIb III
Maintenance of body temperature in a normothermic
range is recommended for most procedures other than
during periods in which mild hypothermia is intended to
provide organ protection (e.g. during high aortic crossclamping)
Perioperative Control of Blood Glucose
Concentration
I IIa IIb III
It is reasonable that blood glucose concentration be
controlled during the perioperative period in patients with
diabetes mellitus or acute hyperglycemia who are at high
risk for myocardial ischemia or who are undergoing
vascular and major surgical procedures with planned ICU
admission.
I IIa IIb III
The usefulness of strict control of blood glucose
concentration during the perioperative period is
uncertain in patients with diabetes mellitus or acute
hyperglycemia who are undergoing noncardiac surgical
procedures without planned ICU admission.
Perioperative Use of PACs
I IIa IIb III
The use of a PAC may be reasonable in patients at risk
for major hemodynamic disturbances that are easily
detected by a PAC. However, the decision must be based
on 3 parameters: patient disease, surgical procedure (i.e.
intraoperative and postoperative fluid shifts), and
practice setting (experience in PAC use and
interpretation of results), because incorrect
interpretation of the data from a PAC may cause harm.
I IIa IIb III
Routine use of a PAC perioperatively, especially in
patients at low risk of developing hemodynamic
disturbances, is not recommended.
Intraoperative and Postoperative Use of
ST-Segment Monitoring
Intraoperative and postoperative ST-segment monitoring
I IIa IIb III can be useful to monitor patients with known CAD or those
undergoing vascular surgery, with computerized ST
segment analysis, when available, used to detect
myocardial ischemia during the perioperative period.
I IIa IIb III
Intraoperative and postoperative ST-segment monitoring
may be considered in patients with single or multiple risk
factors for CAD who are undergoing noncardiac surgery.
Surveillance for Perioperative MI
I IIa IIb III
Postoperative troponin measurement is recommended
in patients with ECG changes or chest pain typical of
acute coronary syndrome
I IIa IIb III
The use of postoperative troponin measurement is not
well established in patients who are clinically stable
and have undergone vascular and intermediate-risk
surgery.
I IIa IIb III
Postoperative troponin measurement is not
recommended in asymptomatic stable patients who
have undergone low-risk surgery.